1. Field of the Invention
The present invention relates generally to resins for use in preparing binders for products formed from mineral fibers, and more specifically, to processes for preparing water-soluble phenol-formaldehyde resins, binders for glass fiber including such resins, and glass fiber products formed using such binders.
2. Brief Description of the Prior Art
Phenolic resins are well known for use in preparing binders for glass fiber products such as thermal and acoustic insulation, glass fiber mats for rein forcement and printed circuit For example, U.S. Pat. No. 3,932,334 discloses phenol-formaldehyde resole resins which are both water soluble and thermosettable, as well as binder systems from such resoles for use in bonding glass fibers to prepare articles such as insulative batts. Typically, in preparing the binder in addition to the water soluble phenolformaldehyde resin, other components such as other resins, monomers, and additives are also included. Substantial proportions of nitrogenous resins, such as urea-formaldehyde and melamine-formaldehyde resins, and/or monomers such as urea, melamine and dicyandiamide, which are condensible with the phenol-formaldehyde resins can be included. Typically, after the binder is applied the glass fibers heat is applied to volatilize the aqueous solvent and to cure the binder.
In practice, because the binder has a relatively short storage life (on the order of hours), it is usually prepared shortly before use at the glass fiber production facility. On the other hand, the water soluble phenol-formaldehyde resin can have somewhat greater storage stability (on the order of days or weeks), and it is highly desirable to prepare the phenol-formaladehyde resin where the highly reactive raw materials are available and subsequently to transport the resin to the glass fiber production facility rather than ship phenol and formaldehyde to the manufacturing site.
The phenol-formaldehyde resin is prepared by reaction between phenol and formaldehyde in aqueous solution under basic conditions. A catalyst is employed to promote the methylolation of phenol. Catalysis by alkali or alkaline earth metal bases is well known, see, for example, U.S. Patent 2,676,898. It is known that use of calcia yields a number of favorable result, such as improved resinification efficiency and increased application efficiency and curability of binders formulated with such resins. While other alkaline earth metal bases, principally barium hydroxide such as discussed in British Patent 905,393, have been used as catalysts in preparing phenol-formaldehyde resins, use of calcium bases is strongly favored by cost considerations.
In preparing the phenol-formaldehyde resin the basic aqueous solution is typically neutralized after the desired extent of resinification has been achieved. A significant disadvantage encountered in using calcium bases for catalyzing the reaction of phenol and formaldehyde to form resole resins has been the low aqueous solubility of calcium salts formed when the reaction mixture is neutralized. U.S. Patent 3,624,247 discloses removal of calcium ions from phenol-formaldehyde resin solutions by addition of an ammonium salt including an anionic species which forms an insoluble precipitate with calcium. However, while the neutralization can be carried out in a manner which promotes formation of fine particulates of insoluble calcium salts, the presence of any such particulate is undesirable. The particulate may settle out of the resole solution during storage, complicating transfer of the resole solution and preparation of the binder. A significant problem may be encountered should the particulate clog lines or nozzles used to apply the binder to the glass fibers. While the particulate could in theory be removed by physical means, for example filtration, centrifugation, decantation or the like, such additional preparative steps could significantly increase the cost of the resole product. In addition, physical separation of the precipitate would be likely to reduce the yield of resole resin and produce an uncured resole-precipitate byproduct which would have to be disposed of in an environmentally sound manner. A simpler resolution of the problem is needed.
Recently, it has been proposed to adjust the pH of the resin solution to between 7.5 and 11.0 and to slowly add sulfate in the form of sulfuric acid or ammonium sulfate to form a complex with the calcium ions. According to the disclosure of U.S. Pat. No. 4,650,825, the complex is stable for at least several hours, permitting preparation of a binder with the resole solution and subsequent application of the binder to glass fiber to form a bonded product. However the stability of the calcium complex is limited, and it is impractical to prepare a phenol-formaldehyde resin by this method off-site and to subsequently ship the resin to the production facility where it will be consumed, as precipitation is likely to occur before the binder can be applied. A longer-lived solution to the problem is desirable.